1. Field of the Invention
This invention relates generally to friction clutches and more particularly to friction clutch discs.
2. Background Information
German Laid Open Patent Application No. 3 921 283, which corresponds to U.S. Pat. No. 5,016,744 entitled "Clutch Disc for a Friction Clutch", discloses such a clutch disc. On that clutch disc, there is a basic friction device, which is located between the end surface of the hub toothing and the one cover plate. It consists of a friction ring which is in direct contact with the toothing, and a lock washer between the friction ring and the cover plate.
Basic friction devices of this type are tuned so that they generate the friction force in the idle range. But the range of fluctuation for the friction force generated by such a configuration is too great for particularly difficult tunings. With such a design, it cannot be guaranteed that the same friction surface will always act to apply the friction. In particular, it is easily possible for the friction surface to change, namely from the toothing of the hub to the friction ring, from the friction ring to the spring, or from the spring to the cover plate. Even if the coefficient of friction of the friction ring in relation to steel is lower than the coefficient of friction for steel-on-steel, if there is any surface roughness, the friction surfaces can occur between the lock washer and the cover plate, at least temporarily.
The change of the friction surface, which occurs in known clutch assemblies has a very significant disruptive effect on idle tuning in sensitive vehicles.